The present invention relates to an improvement in a mechanism for adjusting a rotational balance of a precision cutting machine such as dicing machine (dicer).
In the production of semiconductor devices, for example, a surface of a semiconductor wafer of nearly a disk shape is sectioned into a plurality of rectangular sections by cutting lines called streets that are arranged in a lattice pattern, and predetermined circuit patterns are formed on the rectangular sections. The plurality of rectangular sections to which the circuit patterns are given are cut and separated individually to form so-called semiconductor chips. The semiconductor wafer is usually cut by a precision cutting machine called dicing machine.
The above cutting machine comprises a spindle unit having a rotary spindle, a securing flange mounted on an end of the rotary spindle and having a tool-mounting portion along the outer periphery thereof, an annular cutting tool having a mounting hole that fits to the tool-mounting portion of the securing flange, and a holding flange for holding the cutting tool in cooperation with the securing flange, and the cutting tool rotating at a high speed (e.g., 60,000 rpm) cuts a workpiece. In cutting the semiconductor wafer, in particular, a grinder blade constituting a cutting tool having a thickness of about 15 xcexcm is required to be positioned on the cutting line having a width of about 50 xcexcm formed on the semiconductor wafer to effect the cutting with high precision. For this purpose, vibration of the blade must be avoided.
To facilitate the attachment or detachment of the cutting tool mounted on the rotary spindle, a small clearance of about several microns must be provided between the mounting hole of the blade and the tool-mounting portion of the securing flange attached to the rotary spindle. When the cutting tool is mounted in a state of the center of rotation of the rotary spindle not being in agreement with the center of rotation of the cutting tool, therefore, the rotational balance is not attained and hence, vibration occurs as the rotary spindle and the blade rotate at high speeds. Vibration produces a lot of pitching on both sides of the cutting groove cut by the grinder blade that constitutes the cutting tool, making it difficult to accomplish the cutting with high precision. The same problem occurs even when the rotational balance of the cutting tool itself is not maintained.
In order to solve the above-mentioned problem, the cutting machine is equipped with a mechanism for adjusting the rotational balance to adjust the rotational balance after the cutting tool is mounted on the rotary spindle. According to a conventional mechanism for adjusting the rotational balance as shown in FIG. 11, a holding flange 03 holding a cutting tool 02 in cooperation with a securing flange (not shown) attached to an end of a rotary spindle 01 is provided with a plurality of threaded holes 04 at even intervals in the axial direction for mounting a weight for adjusting the balance and then, after the cutting tool 02 is mounted on the rotary spindle 01, plural kinds of balance weight screws 05 having different weights are screwed into the plural threaded holes 04 to adjust the rotational balance.
In the above-mentioned conventional mechanism for adjusting the rotational balance, however, plural kinds of balance weight screws 05 having different weights must be prepared for precisely adjusting the rotational balance. Besides, the threaded holes 04 and the balance weight screws 05 are so small that they require cumbersome handling, and a considerable degree of skill is required for adjusting the balance.
It is an object of the present invention to provide a mechanism for adjusting a rotational balance of a cutting machine, which can facilitate the precise adjustment of balance without the need of preparations of plural kinds of balance weight screws.
In order to accomplish the above-mentioned object according to the present invention, there is provided a mechanism for adjusting a rotational balance of a cutting machine, which comprises a spindle unit having a rotary spindle, a securing flange mounted on an end of the rotary spindle and having a tool-mounting portion along the outer periphery thereof, an annular cutting tool having a mounting hole that fits to the tool-mounting portion of the securing flange, and a holding flange for holding the cutting tool in cooperation with the securing flange, wherein:
at least two threaded holes are formed in the outer periphery of the holding flange in the radial direction, and balance weight screws are screwed into the threaded holes; and
the balance weight screws are suitably moved forward or moved back along the threaded holes in the radial direction to adjust the rotational balance of the spindle unit.
According to the present invention, furthermore, there is provided a mechanism for adjusting a rotational balance of a cutting machine, which comprises a spindle unit having a rotary spindle, a securing flange mounted on an end of the rotary spindle and having a tool-mounting portion along the outer periphery thereof, an annular cutting tool having a mounting hole that fits to the tool-mounting portion of the securing flange, and a holding flange for holding the cutting tool in cooperation with the securing flange, wherein:
at least two threaded holes are formed in the outer periphery of the securing flange in the radial direction, and balance weight screws are screwed into the threaded holes; and
the balance weight screws are suitably moved forward or moved back along the threaded holes in the radial direction to adjust the rotational balance of the spindle unit.